The present invention relates to mechanisms for driving wiper systems, and in particular relates to ball joints for use in mechanisms for driving a pair of wipers using a single motor.
Windshield wipers for passenger automobiles are usually provided in pairs driven in tandem by a linkage and powered by a single motor. A rotary drive crank or eccentric driven by the motor is connected through connecting rods to levers that move wiper arm pivot shafts reciprocatingly through limited arcs. Ball joints are used to attach the connecting rods to the drive crank and the lever connected with each wiper arm shaft, and the drive crank is rotated continuously to provide continuous reciprocating pivoting movement in the wiper arms. With a single eccentric or drive crank used to control a pair of wiper arms, each connecting rod is typically connected to the eccentric crank pin through a separate ball joint.
The wiper arm pivot shafts may not be parallel with one another nor with the drive crank shaft, and so connection through the use of ball joints is necessary. Both ball joints must be on the same side of the crank arm in order for the crank to avoid interference with the motor. Conventionally, two ball joints are mounted on a single crank pin carried by the eccentric drive crank arm. Such a conventional arrangement of a pair of ball joints is shown, for example, in Schmid, et al., U.S. Pat. No. 3,749,341 and Stinson, U.S. Pat. No. 5,473,355.
Mounting a pair of ball joints alongside one another on a crank pin creates a significant lever arm length between the further one of such ball joints and the eccentric drive crank arm in which the crank pin is mounted. This long coupling may result in less precise drive of the wipers than is desired. In operating large wipers, for wiping large windshields such as those on large trucks, motor homes, industrial and agricultural equipment, buses, or ships, the forces carried through the connecting rods, when applied through the lever arm provided by such a crank pin and a pair of ball joints, may result in excessive amounts of stress applied to the eccentric drive crank arm.
French Patent No. FR2789132, assigned to Peugeot Citroen Automobiles SA, discloses a ball joint connection including a single ball to drive two connecting rods. A first connecting rod is mated to the ball by a first socket having a convex exterior surface over which a second socket is mated, to attach a second connecting rod to the single ball. However, since the sockets are of resilient plastic material and apparently merely snap resiliently into a mating relationship, the assembly thus provided may be subject to separation or failure under load, and thus may not be capable of carrying larger loads which may be imposed through use of such of a connection in a wiper system including large wipers.
What is desired, then, is an improved close-coupled ball joint through which a single ball can drive a pair of connecting members, which is able to carry large loads without failure, and which, nevertheless, can be manufactured at a reasonable cost.